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2020 IEEE Region 10 Symposium (TENSYMP), 5-7 June 2020, Dhaka, Bangladesh
978-1-7281-7366-5/20/$31.00 ©2020 IEEE
Design of Microstrip Patch Antenna on Rubber
Substrate with DGS for WBAN Applications
Nazmus Sakib
Dept. of Electrical and Computer
Engineering
International Islamic University
Malaysia
Kuala Lumpur, Malaysia
sakib.iium17@gmail.com
Md. Shazzadul Islam
Dept. of Electrical and Computer
Engineering
International Islamic University
Malaysia
Kuala Lumpur, Malaysia
shazzadulislam@mail.ru
Siti Noorjannah Ibrahim
Dept. of Electrical and Computer
Engineering
International Islamic University
Malaysia
Kuala Lumpur, Malaysia
noorjannah@iium.edu.my
M. M. Hasan Mahfuz
Dept. of Electrical and Computer
Engineering
International Islamic University
Malaysia
Kuala Lumpur, Malaysia
mahfuz216@gmail.com
Muhammad Ibn Ibrahimy
Dept. of Electrical and Computer
Engineering
International Islamic University
Malaysia
Kuala Lumpur, Malaysia
ibrahimy@iium.edu.my
Abstract— The physical flexibility has a significant impact
on microstrip antenna design for wireless body area network
(WBAN) application and designing such an antenna on a flexible
substrate has many challenges. This paper presents an inset-fed
microstrip patch antenna designed on a rubber substrate with
defected ground structure (DGS). DGS is used to further
enhance the antenna performances. The designed antenna is
expected to operate at 2.45 GHz within the ISM band range and
the return loss is -37.33dB with wide –10dB bandwidth of
101MHz. In addition, the VSWR value is 1.03 at the resonant
frequency with an increase of 7.5% in the realized gain
compares to the antenna without DGS. The accumulated surface
current is 174 A/m on the radiating patch with a maximum
realized gain of 3.42 dB and the maximum radiation efficiency
of more than 60%. The antenna design, simulation, and
performance analysis have been conducted using Computer
Simulation Technology (CST) software. This paper focuses on
the improvement in the return loss and antenna operating
bandwidth of the flexible antenna to make it suitable for WBAN
application.
Keywords— Rubber substrate, WBAN, Inset-Fed Microstrip
Patch Antenna, DGS, CST microwave studio.
I. I
NTRODUCTION
At present, flexible wearable antenna has a very important
role for body area network (BAN) applications. Antenna is a
basic tool in communication which is used to transmit signal
wirelessly. It can transmit the data from one device to another
device by propagate the signals on air space. It has widely
acceptance in medical system as health monitoring, human
activity monitoring, pressure monitoring, and besides that
uses also in sports, navigation, wearable computing etc.
However, developing a flexible wearable antenna is
extremely challenging due to the degradation of antenna
performance when operating on human body. This issue is
being considered to resolve the rigidity problem and improve
the antenna performance during changes in the human body
posture and body movement [1].
Consequently, many research works have been conducted
to develop new substrate for flexible antenna particularly in
material its elasticity. Many studies conducted are on plastic,
rubber, textile, paper, PDMS and various natural materials.
Rubber material is a type of natural polymer and it was chosen
as a suitable antenna substrate due to its’ wide stretch ratio,
good chemical stability, high resilience, good weather ability,
heat resistance, waterproof and can easily comply with bent
surfaces. Above all, the most significant fact that rubber is
extracted naturally, and it is environment-friendly [2].
Works done by [3], demonstrated significant enhancement
on is due to the filler content. The permittivity can be varied
through the inclusion of carbon black (CB) in rubber substrate
as reliable filler material. Moreover, the composition of rubber
substrate with carbon black can enhance the RF performance
and can be implemented [4]. The bending tests conducted in
[3], have resulted with fixed resonance frequency with the
bending direction formed at E-plane and H-plane while the
return loss was -22dB at the flat condition. In contrast, the
observation on that results of this paper [3], the return loss
increased (-14dB & -12dB respect on 160, 60) during the
bent condition. The value of filler content has significantly
affected the microwave characterization of rubber material. It
has leads to the increment of the loss tangent (Tanδ) and
electrical conductivity [5].
In [6], [7], microstrip patch antenna using rubber substrate
with permittivity at 3.1, 1.8 mm thickness were developed
with return losses at -30.92dB and -18dB respectively. The
antenna dimensions have been optimized to attain better result
in [6]. The design was a compact planer dipole antenna with
rubber polymer for WBAN application. It achieved a stable
performance on body condition with various return losses
from -19dB (free space) with the resonant frequency at 2.46
GHz to -20.62dB (on the skin) at 2.44 GHz resonant
frequency. Moreover, the specific absorption rate (SAR)
evaluated in [8] using 1.5mm thick rubber polymer substrate.
The antenna efficiency has varied from 23.21% (at free space)
to 18.30% (skin), 21.57% (on homogeneous) which showed
in [8] this study.
The inset fed microstrip patch antenna has designed in [9]
with DGS structure for ISM band application. The antenna
was constructed using Taconic (TLX-8) substrate where the
material thickness was only 0.5 mm, the dielectric constant
was 2.55 and the loss tangent (Tan δ) at 0.0019 (very few)
respectively. In this paper, it has achieved very good realized
gain at 7.04 dBi and the VSWR at 1.06 only where the
material was very thick to use as substrate. With DGS, the
reflection coefficient (S
11
) was around -30 dB where the return
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loss at the designed antenna without DGS at -13.5dB only with
-10dB bandwidth of 21 MHz [9].
In this paper, it is presented an improvement of return loss
(reflection coefficient S
11
) at the antenna performance on
rubber substrate with defected ground structure (DGS). The
DGS structure improves the surface current, directivity and
better radiation efficiency. The proposed design also improves
the voltage standing wave ratio (VSWR). This paper has
organized as following steps. Section I will discuss about the
Introduction. Section II and III present the Methodology,
Results and Discussion respectively. Lastly; the conclusion is
given in Section IV.
II. METHODOLOGY
In this work, the inset fed microstrip antenna was made using
rubber material as the flexible dielectric layer. The CST
microwave studio was used for antenna design and simulation.
The rubber material was chosen due to its flexibility and
bendable properties but still capable of producing reliable RF
performance. Figure 1 illustrates the designed antenna with
given permittivity and loss tangent are 3.1 & 0.02
respectively.
Figure 1. The proposed antenna design at DGS condition. (a) front view
(patch shape) and (b) back view (ground plane)
This design uses the inset fed microstrip line to improve
return loss. In this proposed microstrip antenna, the thickness
of the rubber substrate is 1.88 mm placed in the middle
between the conductor and ground. Meanwhile, the conductor
and ground layers are made of copper sheet (0.035mm,
thickness). The DGS is located at the ground plane is
intentionally modified for enhancing the antenna
performance.
The required center frequency is 2.45 GHz, with VSWR
of 1.03 (that is near 1) and the difference between two
bandwidth (2.5 and 2.4 GHz) and it is 0.1 GHz. The center of
frequency is 2.45 GHz, which divided by 0.1 GHz for an
antenna Q of 24.5.
The antenna bandwidth (BW) can be calculated by the
following equation (1) [10],
= VSWR − 1
Q√VSWR
(1)
where, Q = The quality factor of an antenna
The antenna can also be characterized based on the return
loss (RL) and antenna gain. With VSWR= 1.03, the return loss
is -36.61dB as described by Equation (2).
(RL) = -20log
10
(r) (2)
here, r = (VSWR − 1)/(VSWR + 1)
The subsequent equations are used to calculate the
microstrip patch antennas extents. The width (W) of the
proposed antenna can calculate by,
= C
2√∈+1
2
(3)
where, = Resonant frequency
εr = Dielectric constant
The width (W) and the length (L) is the main constituents
for calculate an antenna and the characteristics of dielectric
layer effect on antenna design.
= C
2
o√∈ −0.824ℎ(
(∈ + 0.3)(
ℎ+0.264)
(∈ − 0.258)(
ℎ+0.8)
(4)
Here ∈= The effective dielectric constant and it is
calculated using by the subsequent relation,
∈=∈+1
2+
2[1
√
1+12(ℎ
)
] (5)
where, h = substrate height
∈ = effective dielectric constant of substrate.
∆ = 0.412ℎ (∈ + 0.3)(
ℎ+0.264)
(∈ − 0.258)(
ℎ−0.8)
(6)
The radiation power of an antenna can increase by
improving of the width of radiator.
L
=
L
eff
-2∆
L
(7)
The input impedance and the reflection coefficient depend
on inset fed length and width. The resonant frequency will
change due to the variation of inset width (W
if
) and the return
loss will change due to the variation of inset length (L
if
). In
this design, the inset fed length (L
if
) is optimized (using CST
optimizer). In addition, The microstrip fed width (Wf) and the
inset fed width (W
if
) is the same value.
Inset fed length (L
if
) =
cos
(
√
) (8)
The ground length (L
g
) and ground width (W
g
) are
calculated by following formulas [11]:
Wg = 6h+Wp Or Wg = 12h+Wp (9)
L
g
= 6h+L
p
Or L
g
= 12h+W
p
(10)
Table 1 & II present the calculated and optimized values
of the antenna dimensions,
T
ABLE
I.
ANTENNA DIMENSIONS OF PROPOSED DESIGN
Paramet
ers
Lp Wp Lg W
g
Li
f
W
f
i
L
f
W
f
h
Dimensi
ons
(mm) 31.3 42.4 60
55
8
4.6 19.
4
4.6 1.8
T
ABLE
II.
D
IMENSIONS OF THE PROPOSED ANTENNA WITH
DGS
Parameters Ls S S
d
Slr St Ws t
Dimensions
(mm)
8 6 29 10 23 1 0.035
III. R
ESULTS
AND
D
ISCUSSIONS
The calculated patch width (Wp) and patch length (Lp) are
42.76mm and 34.12mm respectively. Using equation (9) &
(10), we get the ground width (Wg) = 53.74 mm and the
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ground length (Lg) = 53.91 mm. The optimization of antenna
parameter implements in proposed design which requires to
improve the antenna efficiency based on importance.
Figure 2 and Figure 3 are showing the return loss, VSWR
respectively. These outputs were obtained from simulation
results by using CST microwave studio.
Figure 2. The return loss (S
11
) of the proposed antenna
Figure 3. The VSWR of the proposed antenna
The return loss of the antenna also known as reflection
coefficient (S parameters) is shown in Figure 2. Here, we get
2.45 GHz resonant frequency, with the return loss of antenna
with DGS is lower than antenna without DGS at -37.33 dB.
At -10 dB, the bandwidth of an antenna is between 2.4004 to
2.502 GHz which is 101 MHz. Without DGS, the value of
return loss, S
11
is only -20.23 dB with the similar resonance
frequency as the antenna with DGS.
In Figure 3, it is shown that the voltage standing wave ratio
(VSWR) for the DGS antenna design is 1.03 (which is near 1)
and that is better VSWR value with respect to the non DGS
antenna. Here, we get a slight distance between DGS and
without DGS values. It can be deduced that an improvement
of VSWR using the DGS method. It demonstrates the
advantage of using DGS on antenna, as it improves the VSWR
value from 1.22 to 1.03. Results in Figure 4 infer that the
antenna with DGS design could have higher radiation
efficiency if compared with non DGS antenna. The radiation
efficiency is -2.464 dB while comparing to another design
without DGS is -3.177 dB and there DGS method leads an
increase of 7.5 % in the realized gain.
The value of increasing of the realized gain can calculate
by the following equations (11) [9].
Increasing (%) =
100 (11)
w
here, G = Gain of an antenna with DGS,
G = Gai
n
of an antenna without DGS
Figure 4. 3D radiation pattern of the designed antenna with DGS
Moreover, with the DGS method, the radiation efficiency
that is -2.464 dB where the total efficiency at -2.489 dB. With
this result, evidently the loss of efficiency is only 0.025 dB.
On the other hand, during without DGS method, the radiation
efficiency is -3.177 dB while total efficiency is -3.248 dB and
here the loss of efficiency is 0.071 dB, which is higher losses
than using DGS method.
Figure 5. Radiation pattern in Polar form of the antenna
The radiation pattern (2D polar form) is shown in Figure
5. The directivity of this antenna is 6.46 dBi and the main lobe
direction is 1
0
deg. Figure 5, represents the single dimension
radiation patterns of the patch antenna using rubber materials
at 2.45 GHz. It is understood that the antenna has a broadside
radiation pattern and the gain also acceptable as shown in the
figure.
In terms of surface current, results of DGS antenna has
bigger value of 174 A/m and this is almost 51 A/m more when
compared with the designed antenna without DGS shown in
Figure 6.
(a)
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(b)
Figure 6. Surface current of the antenna without (a) and with DGS (b)
Meanwhile, the maximum efficiency obtained is around
60%. This value is better than the normal condition shown in
Figure 7.
Figure 7: Radiation efficiency of an antenna at DGS conditio
n
Figure 8, the maximum gain is 3.42 dBi at the selected
bandwidth frequency with DGS condition while the maximum
gain without DGS at 3.18 dBi. The gain of an antenna can
increase by using at DGS condition, the result is 7.5%.
Figure 8. Gain of an antenna at DGS conditio
n
The summary of the discussions mentioned above
regarding the improvement of an antenna is shown in Table
III.
T
ABLE
III.
OUTPUT COMPARISON BETWEEN
DGS
AND WITHOUT
DGS
Name of the experiment With DGS Without DGS
Return Loss (S
11
), dB -37.33 -20.23
Bandwidth (BW), MHz 101 73.9
VSWR 1.03 1.22
Surface Current, A/m 174 123
Total Efficiency -2.489 -3.248
Loss of Efficiency, dB 0.025 0.071
Gain, dBi 3.42 3.18
The comparison between existing works and proposed
antenna have some differences are due to the dielectric
properties, metal thickness, size, substrate, thermal stability,
frequency and so on. Here, the proposed substrate (rubber) has
the highest bandwidth which is BW = 101MHz. By comparing
between DGS and without DGS, it has been proven that the
gain of DGS antenna (at 3.42 dBi) is better than without DGS
(at 3.18 dBi). Moreover, the proposed antenna has greater
return loss which is -37.33dB and this return loss remaining as
better value compared between existing works. This proposed
antenna achieved the maximum efficiency than other existing
works in terms of gain and return loss.
T
ABLE
IV.
C
OMPARATIVE STUDY ON EXISTING WORKS AND PROPOSED
DESIGN
Ref. fr, GHz S
11
, dB Bandwidth, MHz Gain, dBi
[3] 2.45 -23 80 2.3
[5] 2.4 -25 70 -
[6] 1.32 -30.92 20 -
[7] 2.45 -18 100 -
[8] 2.44 -21 100 - 0.96
This Work 2.45 -37.33 101.6 3.42
IV.
CONCLUSION
This paper has described a numerical analysis on antenna
performance of flexible microstrip patch antenna for WBAN
application whereas the primary approaches to use rubber
material as substrate and the center frequency is 2.45 GHz.
Simulation results are presented and described. In this work
an increment of 7.5% of the realized gain was observed using
DGS method. DGS is a technique that can reduce the VSWR,
improve the return loss, increase the surface current, so it can
say the improvement of the antenna performance. In this work,
the enhancement of antenna performances were achieved by
using DGS.
R
EFERENCES
[1] N. Othman, N. A. Samsuri, M. K. A. Rahim, and K. Ka mardin,
“Design and analysis of flexible bow-tie antenna for medical
application,” Elektr.- J. Electr. Eng., vol. 16, no. 1, pp. 17–21,
Apr. 2017.
[2] N. A. M. Affen di, N. A. L. Alias, Z. Awang, M. T. Ali, and A.
Samsuri, “Microwave non-destructing testing of rubber at X-
band,” in 2013 IEEE International RF and Microwave
Conference (RFM), 2013, pp. 333–337.
[3] Z. Awang, N. A. Mohd Affen di, N. A. L. Alias, and N. A. M.
Razali, “Flexible Antennas Based on Natural Rubber,” Prog.
Electromagn. Res., vol. 61, pp. 75–90, 2016.
[4] F. A. Oliveira et al., “Study of the thermomechanical and
electrical properties of conducting composites containing natural
rubber and carbon black,” J. Appl. Polym. Sci., vol. 106, no. 2,
pp. 1001–1006, 2007.
[5] S. H. Dar, J. Ahmed, and M. Raees, “Characterizations of
Flexible Wearable Antenna based on Rubber Substrate,” Int. J.
Adv. Comput. Sci. Appl. Ijacsa, vol. 7, no. 11, 2016.
[6] J. S. Chougule and D. U. V. Wali, “Design of Flexible Microstrip
Antenna for Wearable Application,” vol. 2, no. 6, p. 4, 2015.
[7] J. Kurian, U. Rajan M.N., and S. K. Sukumaran, “Flexible
microstrip patch antenna using rubber substrate for WBAN
applications,” in 2014 International Conference on
Contemporary Computing and Informatics (IC3I), 2014, pp.
983–986.
[8] A. G. Al-Sehemi, A. A. Al-Ghamdi, N. T. Dishovsky, N. T.
Atanasov, and G. L. Atanasova, “Flexible and small wearable
antenna for wireless body area network applications,” J.
Electromagn. Waves Appl., vol. 31, no. 11–12, pp. 1063–1082,
Aug. 2017.
[9] M. S. Islam, M. I. Ibrahimy, S. M. A. Motakabber, and A. K. M.
Z. Hossain, “A Rectangular Inset-Fed Patch Antenna with
Defected Ground Structure for ISM Band,” in 2018 7th
International Conference on Computer and Communication
Engineering (ICCCE), 2018, pp. 104–108.
[10] Y. Huang and K. Boyle, Antennas: From Theory to Practice.
John Wiley & Sons, 2008.
[11] M. S. Islam, M. I. Ibrahimy, S. M. A. Motakabber, A. K. M. Z.
Hossain, and S. M. K. Azam, “Microstrip patch antenna with
defected ground structure for biomedical application,” Bull.
Electr. Eng. Inform., vol. 8, no. 2, pp. 586–595, Jun. 2019.
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